1. Field of the Invention
The present invention relates to a light-emitting device and an image reading apparatus.
2. Related Art
Hitherto, an image reading apparatus (a contact image sensor) is used as an apparatus for reading a document image or the like in a facsimile machine, a copy machine, an image scanner, etc. The image reading apparatus includes a light-emitting device that irradiates light linearly along the main-scanning direction onto a surface of a document, and this light-emitting device in turn includes a transparent light-guiding member having a bar- or plate-like shape with a longitudinal axis. Light incident onto an end surface of the transparent light-guiding member is reflected and transmitted therethrough, and emitted to the outside from an emission surface located along the longitudinal axis. A light-emitting device for use in such an image reading apparatus is illustrated in FIG. 20 (cf. for example, Japanese Patent Application Laid-open No. 1999-330557, page 6, FIG. 10), in which a light-emitting element 3000 is made up of a first lead member 3210, a second lead member 3221, a third lead member 3222, a fourth lead member 3223, and a molded member 3300 on which these lead members are fixedly mounted. A first semiconductor light-emitting element chip 3110, a second semiconductor light-emitting element chip 3120 and a third semiconductor light-emitting element chip 3130 (hereinafter referred to “semiconductor light-emitting element chips 3110, 3120, 3130”) are mounted on the first lead member 3210. The first lead member 3210 has a lead terminal part 3210a for electrical connection to an outside electrode and a mounting part 3210b formed integrally with the lead terminal part 3210a, in which the semiconductor light-emitting element chips 3110, 3120, 3130 are mounted on the mounting part 3210b. The first semiconductor light-emitting element chip 3110 has a first electrode 3111 and a second electrode 3112. The first electrode 3111 and the second electrode 3112 are electrically connected to the first lead member 3210 and the second lead member 3221 by wire, respectively. The second semiconductor light-emitting element chip 3120 also has a first electrode 3121 and a second electrode 3122 that are electrically connected to the first lead member 3210 and the third lead member 3222 by wire, respectively. The third semiconductor light-emitting element chip 3130 also has a first electrode 3131 and a second electrode 3132, in which the second electrode 3132 is electrically connected to the fourth lead member 3223 by wire and the first electrode 3131 is electrically connected to the first lead member 3210 by a bonding material.
The above described conventional light-emitting element 3000 poses a problem in that heat generated from one of the three semiconductor light-emitting element chips, which all are mounted on the first lead member 3210, may break or damage the residual chips. This problem may be caused for example in a case in which an RGB light-emitting element is produced by using a GaN semiconductor light-emitting element chip that emits blue light for the first semiconductor light-emitting element chip 3110, a GaN semiconductor light-emitting element chip that emits green light for the second semiconductor light-emitting element chip 3120, and a semiconductor light-emitting element chip that emits red light for the third semiconductor light-emitting element chip 3130. The current flowing through the light-emitting element causes the first semiconductor light-emitting element chip 3110 and the second semiconductor light-emitting element chip 3120 to have a higher heat output than the third semiconductor light-emitting element chip 3130, which heat from these chips is transmitted to the third semiconductor light-emitting element chip 3130 via the first lead member 3210 and hence breaks or causes damages to the third semiconductor light-emitting element chip 3130. Especially, heat generated from the semiconductor light-emitting element chips must be taken into account, especially in a case where the light-emitting element is used as a light source for an image reading apparatus, for which a high powered light-emitting element is required.
Hence, it is an object of the present invention to provide a light-emitting device that has an excellent heat release capability and an image reading apparatus using the light-emitting device.